1. Field of the Invention
Apparatuses consistent with present invention relate to recording media, and more particularly, to perpendicular magnetic recording media with a laminated soft magnetic underlayer.
2. Description of the Related Art
Recording density of recording media, such as magnetic disk devices, is rapidly being increased. To increase the recording density of the magnetic disk device, a perpendicular magnetic recording method has been proposed. The recording density of the perpendicular magnetic recording media is increased by magnetization of a magnetic recording layer in a perpendicular direction. The recording layer for such a perpendicular magnetization uses a magnetic material that can display relatively high magnetic anisotropy and coercivity.
To help write data on a recording layer by means of effective magnetization of the recording layer, the introduction of a soft magnetic underlayer (SUL) below the recording layer has been proposed. On the recording layer, a head having a trailing pole and a return pole is generally located for perpendicular magnetization of the recording layer. To obtain the same effect as that of an image head, corresponding to the head having the trailing pole and the return pole, located below the recording layer, the SUL has been introduced.
FIG. 1 is a schematic diagram of a typical perpendicular magnetic recording device.
Referring to FIG. 1, a typical perpendicular magnetic recording medium 10 has an SUL 11, an intermediate layer 13 and a recording layer 15 formed sequentially on a substrate (not shown). On the recording layer 15, a protective layer and/or a lubricant layer, etc. may be further formed. The recording layer 15 is magnetized by a head 20 located at a distance, also known as fly height, above the perpendicular magnetic recording medium 10.
A magnetic flux discharged from a trailing pole 21 upon a writing operation magnetizes the recording layer 15 in a bit region unit and runs along the SUL 11, i.e., enters into and runs along an image head 12, and then returns to a return pole 25. Thus, since a density of the magnetic flux discharged from the trailing pole 21 is effectively transferred to the recording layer 15 without fluctuating, the recording layer 15 is more effectively magnetized by such a magnetic flux.
In the case of introducing such an SUL, a saturation of the SUL should first be considered. SUL saturation leads to degradation of the magnetic flux discharged from the trailing pole because the flux cannot penetrate into the SUL. To effectively prevent the saturation of the SUL, the SUL should have a sufficient thickness and have a sufficient saturation magnetization (MS, SUL). However, a thick SUL can result in serious magnetic domain noise.
Thus, to increase the effect of the introduction of an SUL, studies on forming the SUL in various multilayered structures have been actively performed. In particular, there have been various attempts to prevent spike noise, which accompanies the SUL, or demagnetization due to the movement of a domain wall.